ScienceofSpeed

ScienceofSpeed FAQs > NSX > ENPP > Stroker Engines

Q: What is a stroker engine?

A: The term stroker engine typically refers to an engine that has had an increase over factory of the throw or stroke of the engine's piston.

Q: What are the benefits of a stroked engine?

A: Increasing of the stroke can result in increased torque especially noticed in the lower rev range by increasing the length of time that the force of the combustion is transmitted through the engine to the wheels.

Q: What is the limiting factor of stroke?

A: A few of the limiting factors include:

increased piston speed may affect reliability due to opposing forces placed on components
increased side loading from rod angle may affect piston and cylinder sleeve reliability
increase piston dwell time can affect high engine speed torque

Q: How does ScienceofSpeed build stroked engines?

A: A billet crankshaft is manufactured specifically for the NSX that replaces the factory crankshaft to offer an increased stroke over factory. It is important to realize that the crankshafts that are used are custom made from billet stock, heat treated, and precision ground to exacting specifications. The crankshafts are not reground factory crankshafts with smaller rod journals like offered by other NSX tuners from Japan. The billet made crankshafts are exceedingly high quality used in applications producing more than 200 hp / cylinder and offer an excellent alternative where low volume makes forging unfeasible.

In addition to increasing the stroke of the engine we also increase the bore in most applications allowing greater surface area for the combustion force to act on.

Custom built forged pistons allow the factory forged titanium connecting rods to be used for naturally aspirated built engines while billet rods are available for forced induction applications.

The materials used, tolerances, and balancing most often exceeds Honda's high standards where the factory's production costs are an element as with any production vehicle.

Q: What are the specifications of the ScienceofSpeed stroked engines?

A: Due to using parts custom to these engines, we can produce an engine in a variety of displacements from 3.0L - 3.8L. The factory 3.0L has a 90mm bore x 78mm stroke. The factory 3.2L has a 93mm x 78mm stroke. We can vary the bore by 90-95mm and stroke from 78-88mm. Our most popular naturally aspirated engine sizes are 3.8L (95mm x 88mm) for street use and 3.6L (93mm x 88mm) for road course use. Our most popular engine size for forced induction is 3.5L (93mm x 76mm). In addition, the heads, cams, and other components are reworked specific to the application.

Q: Is forced induction (super/turbocharged) or natural aspiration better?

A: The customer's use and application determines which method for power gain is most suitable. Both methods have advantages and disadvantages and it's too complicated of an issue to say which is better as a general blanket statement. ScienceofSpeed supports and builds solutions for both forced induction and natural aspirated applications.

Natural aspiration is limited by the pressure of the intake charge being at atmospheric pressure. This pressure is introduced into the combustion chamber and squeezed under compression to produce an opposing force under combustion that acts upon the engine's rotating assembly to transmit power to the wheels. Forced induction allows an artificial method of increasing the pressure of this intake charge to maximize mixture density. The higher charge density can in turn place more force on the rotating assembly to transmit more power to the wheels.

Naturally aspirated engines are most often credited for better free revving and tip in throttle response. Forced induction engines rely on a compressor to supply the pressurized charge by engine belt rotation (supercharged) or exhaust pressure. Many road race drivers prefer this throttle response during cornering where the throttle is being modulated rapidly and a linear throttle response eases chassis control.

However, when considering significant power gains (such as more than 20% for the NSX), forced induction can be a much more cost effective solution. In addition, forced induction is capable of producing gains that are physically impossible (especially on standard pump fuel available to most consumers) with naturally aspirated engines.

In scope of the NSX, stroked engines are certainly capable of producing as much if not more power comparable forced induction systems.

example: 3.2L Comptech Supercharger vs. ScienceofSpeed 3.6L
36L-vs-CTSC32L.pdf
3.2L Comptech Supercharger = pink
ScienceofSpeed 3.6L stroker engine = red

However, the referenced stroker engine nears the limit of natural aspiration power for the NSX limited by standard pump gas and currently available induction and exhaust components. Forced induction setups can easily meet and surpass these gains.

example: turbocharged system @ 12 psi vs. ScienceofSpeed 3.6L
36L-vs-turbo12psi.pdf
turbocharged system @ 12psi = blue
ScienceofSpeed 3.6L stroker engine = red

This discussion could be endless touching on the variety of factors that may or may not be important or relevant to your circumstance (race sanctioning body restrictions, the desire to keep the original method of induction in place, etc) and it's a decision that for most customers comes down to personal preference.

Q: What is more reliable? Natural aspiration or forced induction?

A: This is another question where blanket statements such as "natural aspiration is more reliable than forced induction" are made. No one can make a generalized statement like this with out considering the factors of the specific application.

Well designed forced induction systems can be reliable even on vehicles not supercharged or turbocharged from the factory. In general, it has been our experience that forced induction has gained a bad reputation in the aftermarket community because either the system was not designed properly or the system places so much fatigue on the rest of the vehicle's components not designed for this amount of power.

Both causes for poor reliability will affect both natural and forced induction applications. The fact is a very small fraction of modified vehicles of any type producing significantly more power than factory are naturally aspirated. Based on numbers alone, more occurrences of problems with forced induction applications are bound to be discussed.

High output forced induction engines can also be built to be reliable. However, when a high output naturally aspirated engine is built there are three opposing factors. Performance, Reliability, and Cost. Two of the factors always oppose the one remaining. We try to build engines that are balanced somewhere between these three opposing elements. Customers must understand that the increased performance comes at a cost due to the complex materials and techniques used and will not yield the factory priority of reliability.

Q: Can ScienceofSpeed stroked engines be used with super/turbochargers?

A: Absolutely. In forced induction applications, we use a completely different piston design that produces a lower compression ratio and utilizes a larger wrist pin than the naturally aspirated application. This requires us to use a billet connecting rod that results in a maximum stroke of 86mm. We can vary the bore of the engine however our most common size is 93mm to yield a total displacement of 3.5L.